1. Field of the Invention
This invention relates to control of internal combustion engine idling speed.
2. Prior Art
Various idle speed control systems for internal combustion engines are known. Such systems include some which are primarily mechanical and some which are primarily electronic. One of the goals such systems have tried to achieve is to provide increased engine idling stability. However, attempts to react rapidly to changing conditions in order to achieve idling stability may cause an overshoot of desired idling speed or other instability.
U.S. Pat. No. 4,328,775 issued to Ironside teaches a closed loop idling control for an internal combustion engine including a difference signal generator which produces an engine speed error signal. This signal passes through a phase compensator and directly controls the ignition timing to provide a fast loop control of speed. Additionally, the engine speed error signal controls the throttle position through an integrator in a series connection with the phase compensator to provide a slow loop which cancels out the engine speed error to avoid increased exhaust contamination.
U.S. Pat. No. 4,338,899 issued to Geiger et al teaches controlling the ignition timing of a spark ignited internal combustion engine charged with a lean air-fuel ratio to have a stabilized idle speed which is approximately equal to a desired idle speed. The ignition timing of the engine is controlled to linearly advance the timing from a nominal retarded condition in proportion to a change in engine speed below the desired speed. The timing advance may be implemented via a constant time delay and has the same ratio to engine speed changes as the ratio of nominal ignition pulse spacing to the desired engine idle speed.
U.S. Pat. No. 4,344,397 issued to Geiger et al teaches stabilizing engine idle speed by a successive three-stage control system which sequentially regulates ignition timing, fuel quantity and air throughput volume.
U.S. Pat. No. 4,142,483 issued to Ironside teaches an internal combustion engine operation timing control using a programmed read-only memory to produce a multibit digital signal used to determine the instant of operation. One input to the ROM is from a speed counter and the other input to the ROM is from another engine parameter transducer. The digital output of the ROM is applied to a timing counter. A master clock is used for clocking both the speed counter and the timing counter.
U.S. Pat. No. 4,262,643 issued to Cavil et al teaches a timing control system for an internal combustion engine producing a cyclical control pulse offset from a cyclical engine timing reference pulse. The processing circuit includes a counter connected to a NAND gate for producing a control pulse when the counter reaches a preset count, a monostable device subject to the control pulse for resetting the counter, an oscillator for providing preload pulses to the counter for a predetermined period of time to establish a preload count, and a phase-locked loop subject to the reference pulse for transmitting a fixed number of signal pulses per engine revolution to the counter to increment the preload count until the preset count is reached, whereby the control pulse is produced.
U.S. Pat. No. 4,389,989 issued to Hartig teaches an electronic arrangement for idling stabilization between a signal transmitter for ignition spark formation and an ignition device for internal combustion engines. When engine rotational speed decreases, the ignition time point is advanced below a first engine rotational speed, in which there presently is retarded a pulse obtained from the signal transmitter and, with regard to the contemplated unretarded pulse sequence, is transmitted as an advanced signal to the ignition device whereby the unretarded pulses are emitted externally of the stabilization range intermediate the first and a second lower engine rotational speed.
There still remains a need for improved regulation of engine idle speed. In particular, it would be desirable to have faster response to idle speed fluctuations by control of both ignition spark advance and engine air intake volume.